Dental hand-pieces of the type known as "contra-angle" tool holders generally include an elongated tubular housing arranged to be coupled at one end to an enclosure for the drive mechanism of a dental motor and enclosing an aley for a drive shaft which couples to the drive mechanism. At the other end the drive shaft is coupled to a tool shaft, or to a tool clutch, through gears that rotate the tool on an axis transverse to the drive shaft axis, and a stub housing is provided to enclose the tool and the direction-changing gears. Typical of contra-angle tool holders, the stub-housing is provided with openings at both ends, one to receive the tool and the other to give access to mechanism to lock the tool in place. U.S. Pat. No. 3,369,298 shows one example of such contra-angle tool holders; in that example a clutch is permanently rotatably fixed in the stub-housing, and a tool can be removably inserted into the clutch from one end, while a lock mechanism is provided at the other end. In other examples of such contra-angles, the tool is inserted through the housing from the lock-end of the stub-housing, and a removable (e.g: threaded) cap is provided at the same end to perform the lock function. As contra-angles are made smaller, these parts, epecially removable caps, become so small that they are difficult to manipulate and are easily dropped to the floor, and sometimes lost.
An additional impediment to making contra-angles smaller derives from the direction-changing gears that are used in contra-angle hand-pieces of known designs. In some cases a crown gear drives a tool clutch through a ring of gear radially extending from and surrounding the outer side surface of the clutch; an example is shown in Kaltenbach U.S. Pat. No. 2,319,328. In other cases, bevel gears are used for direction changing, in which case the radially-extending bevel gears surround and extend from the outer side surface of the tool holder or clutch; an example of this case is shown in Flatland U.S. Pat. No. 4,053,983.
In a copending application of one of the present applicants and another, Ser. No. 970,468 filed Dec. 18, 1978, it is taught to affix the radially-extending bevel gear ring directly to the shaft of a tool. This improvement allows the elimination of a clutch component. However, room must be provided for a ring of radially-extending gears surrounding the tool shaft, and for some dentists the need to equip an operatory with a set of "no clutch" tools having their own drive gears, in addition to the already existing tools designed for holding in a clutch, may be objectionable.